Federer has won three Grand Slams since the start of 2017, which includes two Australian Open titles.

Roger Federer is the only tennis player who can maintain a high level of confidence despite playing less in a calendar year, according to the former British tennis player Arvind Parmar.

Since the start of 2017, the Swiss ace has changed the schedule that saw him reduce the number of events he played. He won the Australian Open and Wimbledon in 2017. The success in the latter came after he decided to skip the entire clay court season last year.

Federer came back to Melbourne and won the Australian Open in 2018. Before the start of the 2017 calendar year, Federer was written off and a few of them had ruled out his chances of winning the Grand Slam.

He has proved his critics wrong and went on to win three Grand Slams to extend his overall tally to 20 titles. A semi-final berth at the ongoing Rotterdam Open will help the 36-year-old to beat Rafael Nadal to become the new world No.1.

Parmar heaped praise on Federer for continuing to win major tournaments and claims he is the only player who is capable of achieving such a feat, even after going away for weeks or months.

"It's quite amazing isn't it and I guess we shouldn't lose sight at how incredible it is that at the age of 36 he's still playing at the level he is," Parmar said on Sky Sports, as quoted by the Express.

"It's just a testament to his immense talent and how he has worked so diligently off the court, keeping the body in order after all these years.

"Tweaking the schedule as he's gone along, playing less and seeming to get better and better.

"Not losing confidence because he's not playing as much. He's the only player in my mind who is able to do that. To come back after weeks off, six months off, and come back as if he's never been away. It's quite remarkable."

Federer claimed his 20th Grand Slam at the 2018 Australian Open.Getty Images